1. Description of the geometries studied

1.1 Duct dies

They are used in extrusion blow-molding to produce thin films (between 10 and 300 μm).

• The most commonly used have a helical geometry (figure 1 ). The polymer melt arrives at the lower part of the die via the inlet channel, and is distributed around the die periphery via a series of radial channels, each of which opens out into a helical channel machined around the die. The depth of this channel decreases as the die progresses from bottom to top, while the clearance between the die and the die housing increases. In this way, the polymer is distributed evenly around the periphery of the die, while avoiding weld seams.